I know this is hot topic, so I get right to it. I recently bought a 5d mark 3 with the 24-105 kit lens. Until the 24-70 V2 comes out, I also needed a prime for indoors, so I decided to get both the Canon 50mm F1.4 and Sigma 50mm F1.4 at first. After about 2 days of usage, I returned the Canon. It was so bad that its not even worth talking here. I'm not sure who pays $350 for that lens when for $90 more you can get the Sigma, which is much better than Canon. Just the colors and contrast alone, Sigma was superior to the Canon.

Unfortunately, Sigma also has its faults. Wide open, it's very soft. It's also back focusing extremely bad. There is no way to use this lens between F1.4 - F2.0 if you are closer to your subject for less than 5ft.

Next, I got the Canon 50mm F1.2L. I wasn't going to buy this lens as I thought I'd be happy with Sigma, but as that wasn't the case, I wanted to give it a try. I read a lot about this lens (and the other two as well), the focus shifting issues, the 3ft distance limit, etc. They might be true for certain people, but they certainly weren't for me. First of all, the lens is SHARP, it's so sharp, the minute you put it next to Sigma at 100% crop, it makes Sigma look like a joke.

But I didn't want to give up that easy. Sigma had 2 issues. Sharpness and back focusing. So I tried another 2 days and 2 other copies of Sigma (3 copies total) with hours of micro focus adjustments and moire testing. Unfortunately, all Sigmas had the same sharpness problem. They are just not sharp at all until F2.0. After F2.0 they start getting to acceptable levels (but still not F1.2L levels). Sharpness aside, 2 of the lenses had to be MFA to +20. Even then they were a little off, but that was the maximum the camera allowed. The third one was so bad that even +20 didn't help.

With Canon, there is no MFA, nothing. It focuses right on, no issues. Not even +1/-1 MFA is necessary, it's just simply amazing. You get what you pay for. It's colors are also much better, so is the sharpness (as I already said it many times).

What I want to mention to the potential buyers of these lenses are, there is worlds of difference between these three lenses. Canon F1.4 to me should be given with the Rebel cameras as a cheap kit lens. It's not worth $350, maybe $200 at most. Sigma is very good and if you are not using a full frame camera and you won't have to get close to your subjects and you are okay with non-crop images, it should be fine. Canon F1.2 is something else. The minute you put them side by side with 100% crop, you see the difference.

I think if you CAN afford the L, you definitely should get it, it's a no brainer. If you cannot afford it, then you don't need to read this, you are just stuck with the Sigma in which case you shouldn't call the L overpriced.